Java - Copying one file to another

Introduction
This example illustrates how to copy contents from one file to another file. This topic is related to the I/O (input/output) of java.io package.
In this example we are using File class of java.io package. The File class is an abstract representation of file and directory pathnames. This class is an abstract, system-independent view of hierarchical pathnames. An abstract pathname has two components:

1. An optional system-dependent prefix string,
   such as a disk-drive specifier, "/" for the UNIX root directory, or "\\" for a Win32 UNC pathname, and
2. A sequence of zero or more string names.

Explanation
This program copies one file to another file. We will be declaring a function called copyfile which copies the contents from one specified file to another specified file.
copyfile(String srFile, String dtFile)
The function copyfile(String srFile, String dtFile) takes both file name as parameter. The function creates a new File instance for the file name passed as parameter
File f1 = new File(srFile);
File f2 = new File(dtFile); 
and creates another InputStream instance for the input object and OutputStream instance for the output object passed as parameter
InputStream in = new FileInputStream(f1);
OutputStream out = new FileOutputStream(f2); 
and then create a byte type buffer for buffering the contents of one file and write to another specified file from the first one specified file.

byte[] buf = new byte[1024];
// For creating a byte type buffeR
out.write(buf, 0, len); // For writing to another specified file from buffer buf
Code of the Program : 

import java.io.*;
 


public class CopyFile{

  private static void copyfile(String srFile, String dtFile){
 
    try{
 
     File f1 = new File(srFile);

      File f2 = new File(dtFile);

      InputStream in = new FileInputStream(f1);
   

//For Append the file.
//

OutputStream out = new FileOutputStream(f2,true);
//For Overwrite the file.
      OutputStream out = new FileOutputStream(f2);


        byte[] buf = new byte[1024];
  
    int len;
 
     while ((len = in.read(buf)) > 0){
  
      out.write(buf, 0, len);
 
     }
 
     in.close();

      out.close();
 
     System.out.println("File copied.");
 
    }
 
   catch(FileNotFoundException ex){
      
   System.out.println(ex.getMessage() + " in 
                            the specified directory.");
  
    System.exit(0);

    }
 
   catch(IOException e){
  
    System.out.println(e.getMessage());  
    
    }

  }

  public static void main(String[] args){
 
   switch(args.length){
 
      case 0: System.out.println("File has not mentioned.");

            System.exit(0);
 
     case 1: System.out.println("Destination file has not mentioned.");

            System.exit(0);

      case 2: copyfile(args[0],args[1]);
 
         System.exit(0);

      default : System.out.println("Multiple files are not allow.");
 
           System.exit(0);

    }

  }

} 

Output of program:
Here the data of "Hello.java" file is copied to the Filterfile.txt file.

C:\nisha>javac CopyFile.java C:\nisha>java CopyFile a.java Filterfile.txt File copied. C:\nisha>

You can even use this program for copying files from one hard drive to another hard drive.
Download File Copy Example